CrossC2 Framework Expands Cobalt Strike Threat to Linux and macOS Systems

TL;DR

Japan’s Computer Emergency Response Team Coordination Center (JPCERT/CC) has uncovered a new cybersecurity threat: the CrossC2 framework, which extends the capabilities of Cobalt Strike Beacon to Linux and macOS systems. This cross-platform expansion allows hackers to control and exploit systems beyond Windows, marking a significant escalation in cyber threats. The attacks were observed between September and December 2024, targeting organizations across multiple sectors.

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Introduction

Cybersecurity threats are evolving at an unprecedented pace, and attackers are constantly refining their tools to bypass traditional defenses. One such advancement is the use of the CrossC2 framework, a command-and-control (C2) tool designed to extend the functionality of Cobalt Strike Beacon—a popular penetration testing tool often abused by cybercriminals. Recently, Japan’s CERT Coordination Center (JPCERT/CC) revealed that this framework is being used to target Linux and macOS systems, expanding the threat landscape beyond Windows environments.

This article explores the mechanics of CrossC2, its implications for cross-platform cybersecurity, and why organizations must adapt their defenses to mitigate this growing risk.

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What Is CrossC2?

CrossC2 is a command-and-control (C2) framework that enables attackers to extend the reach of Cobalt Strike Beacon—a legitimate red-team tool frequently repurposed for malicious activities. Traditionally, Cobalt Strike has been limited to Windows systems, but CrossC2 bridges this gap by allowing attackers to:

• Control Linux and macOS systems using Cobalt Strike Beacon.
• Bypass security measures designed for Windows-only threats.
• Execute cross-platform attacks with greater stealth and efficiency.

By leveraging CrossC2, threat actors can now orchestrate attacks across multiple operating systems, making it harder for organizations to detect and respond effectively.

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JPCERT/CC’s Findings: A Cross-Platform Threat

In a report published on August 14, 2025, JPCERT/CC detailed its observations of CrossC2-related incidents between September and December 2024. Key findings include:

• Targeted Systems: While Cobalt Strike has historically focused on Windows, CrossC2 enables attacks on Linux servers and macOS workstations, which are commonly used in enterprise environments.
• Attack Vectors: The framework allows attackers to exfiltrate data, deploy additional payloads, and maintain persistence across diverse systems.
• Evasion Techniques: CrossC2 employs encrypted communication channels and polymorphic code to evade detection by traditional security tools.

This expansion of Cobalt Strike’s capabilities underscores the need for cross-platform threat detection and unified security strategies.

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Why CrossC2 Poses a Significant Risk

The adoption of CrossC2 by cybercriminals introduces several challenges for cybersecurity professionals:

1. Broader Attack Surface: Organizations using Linux and macOS alongside Windows are now at higher risk, as attackers can exploit vulnerabilities across all three platforms.
2. Increased Stealth: CrossC2’s ability to mimic legitimate traffic and use encrypted communications makes it difficult for security teams to identify malicious activity.
3. Resource Drain: Defending against cross-platform threats requires additional monitoring, advanced threat detection tools, and specialized expertise, which may strain IT resources.

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Mitigation Strategies for Organizations

To defend against CrossC2 and similar cross-platform threats, organizations should implement the following measures:

1. Enhance Endpoint Detection and Response (EDR)

• Deploy cross-platform EDR solutions capable of detecting anomalies across Windows, Linux, and macOS.
• Use behavioral analysis to identify suspicious activities, such as unusual network connections or privilege escalations.

2. Strengthen Network Security

• Implement network segmentation to limit lateral movement in case of a breach.
• Use intrusion detection systems (IDS) to monitor for signs of C2 communication.

3. Regularly Update and Patch Systems

• Ensure all operating systems, applications, and security tools are up-to-date to prevent exploitation of known vulnerabilities.

4. Conduct Cross-Platform Threat Hunting

• Proactively search for indicators of compromise (IOCs) related to Cobalt Strike and CrossC2 across all systems.
• Use threat intelligence feeds to stay informed about emerging attack techniques.

5. Educate Employees on Cybersecurity Best Practices

• Train staff to recognize phishing attempts and social engineering tactics, which are often used to deploy C2 frameworks.

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The Future of Cross-Platform Cyber Threats

The emergence of CrossC2 signals a shift in cybercriminal strategies, with attackers increasingly focusing on multi-platform exploitation. As organizations adopt diverse IT environments, the need for unified security solutions becomes critical. Future trends to watch include:

• More Advanced C2 Frameworks: Attackers will likely develop even more sophisticated tools to evade detection.
• AI-Driven Attacks: The use of artificial intelligence to automate and optimize cross-platform attacks.
• Regulatory Responses: Governments and cybersecurity agencies may introduce new guidelines to address cross-platform threats.

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Conclusion

The CrossC2 framework represents a significant evolution in cyber threats, enabling attackers to extend the reach of Cobalt Strike Beacon to Linux and macOS systems. With JPCERT/CC’s findings highlighting active exploitation, organizations must adapt their defenses to combat this cross-platform risk. By implementing proactive detection, network security, and employee training, businesses can mitigate the impact of CrossC2 and similar threats.

As cybercriminals continue to innovate, staying ahead requires continuous vigilance, advanced tools, and a unified approach to cybersecurity.

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Additional Resources

For further insights, check:

• JPCERT/CC Official Report on CrossC2
• Cobalt Strike: Understanding the Threat
• MITRE ATT&CK Framework: Cross-Platform Techniques